It has been estimated that between 10 and 15 percent of the population has chronic Primary Insomnia. Thus, in the United States alone between 27 and 41 million people suffer from a disorder that diminishes their quality of life, negatively impacts on their work performance and puts them at increased risk for medical and psychiatric illness. The economic costs associated with insomnia are estimated to be in the tens of billions of dollars per annum. Despite its prevalence and consequences, little is known about the pathophysiology of insomnia and how it is related to the presenting symptoms of the disorder. Recent work on the spectral components of the sleep EEG show that Beta frequency EEG activity at/around sleep onset and during NREM sleep is increased in patients with Primary Insomnia, in comparison to both good sleeper controls and MDD patients with secondary insomnia. While this suggests that patients with Primary Insomnia exhibit higher than normal levels of CNS arousal at sleep onset and during NREM sleep, little is known, about whether high frequency EEG activity in insomnia is 1) limited to the Beta activity, 2) actually CNS in origin 3), if CNS in origin, preponderant at specific EEG sites, 4) varies with symptom intensity and 5) correlated with the subjective perception of sleep quality and quantity. We propose to undertake one experiment in which three groups of subjects will be studied polysomnographically for four consecutive nights. The subject groups will be 30 patients with Primary Insomnia, 30 patients with insomnia secondary to Major Depression, and 30 good sleeper controls. Digital EEG data from each night of study will be obtained from 10 sites (F3,F4,C3,C4,T5,T6,P3,P4,O1 ,02) and power spectral data will be compiled for each of the first 4 NREM and REM cycles and for each stage of sleep. Group differences for Beta-I (14-20Hz), Beta-2 (20-35Hz), Gamma (35-45Hz) and Omega (45-125 Hz) will be assessed taking into account site-to-site and night-to-night variability. In addition, we will evaluate the extent to which high frequency activity is associated with the perception of sleep quality and quantity.